The present invention relates generally to spin-on glass materials and more specifically to light-absorbing spin-on glass materials for use as anti-reflective layers in photolithography and methods of producing the materials.
To meet the requirements for faster performance, the characteristic dimensions of features of integrated circuit devices have continued to be decreased. Manufacturing of devices with smaller feature sizes introduces new challenges in many of the processes conventionally used in semiconductor fabrication. One of the most important of these fabrication processes is photolithography.
It has long been recognized that linewidth variations in patterns produced by photolithography can result from optical interference from light reflecting off an underlying layer on a semiconductor wafer. Variations in photoresist thickness due to the topography of the underlying layer also induce linewidth variations. Anti-reflective coatings (ARC) applied under a photoresist layer have been used to prevent interference from reflection of the irradiating beam. In addition, anti-reflective coatings partially planarize the wafer topography, helping to improve linewidth variation over steps because the photoresist thickness is more uniform.
Organic polymer films, particularly those that absorb at the i-line (365 nm) and g-line (436 nm) wavelengths conventionally used to expose photoresists, and at the recently used 248 nm wavelength, have been employed as anti-reflective coatings. However, the fact that the organic ARC""s share many chemical properties with the organic photoresists can limit usable process sequences. Furthermore ARC""s may intermix with photoresist layers. One solution to avoid intermixing, is to introduce thermosetting binders as additional components of organic ARC""s, as described, for example in U.S. Pat. No. 5,693,691 to Flaim et al. Dyes may also be incorporated in organic ARC""s, as well as, optionally, additional additives such as wetting agents, adhesions promoters, preservatives, and plasticizers, as described in U.S. Pat. No. 4,910,122 to Arnold et al.
Silicon oxynitride is another material that has been used as an anti-reflective coating. However, silicon oxynitride works as an ARC by a destructive interference process rather than by absorption, which means that very tight control of the oxynitride thickness is necessary and that the material may not work well as an ARC over highly variable topography. Furthermore, silicon oxynitride is typically deposited by chemical vapor deposition, while photoresist layers are typically applied using a spin-coater. The additional chemical vapor deposition process can add to processing complexity.
Another class of materials that can be used as an anti-reflective layer is spin-on-glass (SOG) compositions containing a dye. Yau et al., U.S. Pat. No. 4,587,138, disclose a dye such as basic yellow #11 mixed with a spin-on-glass in an amount approximately 1% by weight. Allman et al. U.S. Pat. No. 5,100,503 disclose a cross-linked polyorganosiloxane containing an inorganic dye such as TiO2, Cr2O7, MoO4, MnO4, or ScO4, and an adhesion promoter. Allman additionally teaches that the spin-on-glass compositions also serve as a planarizing layer. However, the spin-on-glass, dye combinations that have been disclosed to date are not optimal for exposure to the deep ultraviolet, particularly 248 and 193 nm, light sources that are coming into use to produce devices with small feature sizes. Furthermore, not all dyes can be readily incorporated into an arbitrary spin-on-glass composition.
Therefore, an absorbing spin-on-glass anti-reflective coating and lithography material that absorbs strongly and uniformly in the ultraviolet spectral region and a method of producing the spin-on glass anti-reflective coating would be desirable. It would also be desirable for the ARC layer to be impervious to photoresist developers.
An anti-reflective coating material for deep ultraviolet photolithography comprises one or more organic absorbing compounds incorporated into a spin-on-glass (SOG) material. The spin-on-glass materials comprise silicon-based compounds, such as methylsiloxane, methylsilsesquioxane, phenylsiloxane, phenylsilsesquioxane, methylphenylsiloxane, methylphenylsilsesquioxane, silicate polymers and mixtures thereof. As used herein, the group known as xe2x80x9cspin-on-glass materialsxe2x80x9d also comprises siloxane polymers, hydrogensiloxane polymers of the general formula (H0-1.0SiO1.5-2.0)x and hydrogensilsesquioxane polymers, which have the formula (HSiO1.5)x, where x is greater than about four. Also included are copolymers of hydrogensilsesquioxane and alkoxyhydridosiloxane or hydroxyhydridosiloxane. Spin-on-glass materials additionally include organohydridosiloxane polymers of the general formula (H0-1.0SiO1.5-2.0)n(R0-1.0SiO1.5-2.0)m, and organohydridosilsesquioxane polymers of the general formula (HSiO1.5)n(RSiO1.5)m, where m is greater than zero and the sum of n and m is greater than about four and R is alkyl or aryl.
Absorbing compounds suitable for incorporation into the spin-on-glass materials are strongly absorbing at wavelengths less than 375 nm or less than about 260 nm. In particular, suitable absorbing compounds absorb light around wavelengths such as 248 nm, 193 nm, 157 nm or other ultraviolet wavelengths, such as 365 nm, that may be used in photolithography. The chromophores of suitable compounds typically have at least one benzene ring, and in those instances where there are two or more benzene rings, those rings may or may not be fused. Incorporatable absorbing compounds have an accessible reactive group attached to the chromophore, wherein the reactive groups can include hydroxyl groups, amine groups, carboxylic acid groups, and substituted silyl groups with silicon bonded to one, two, or three alkoxy group or halogen atom substituents. The reactive groups may be directly bonded to the chromophore or the reactive groups may be attached to the chromophore through a hydrocarbon bridge or an oxygen linkage. The chromophores may also comprise silicon-based compounds or polymers similar to those used to formulate the spin-on glass materials.
Examples of suitable incorporatable organic absorbing compounds include those compounds with one benzene ring, such as phenyltrialkoxysilane (phenyltriethoxysilane, phenyltrimethoxysilane, phenyltripropoxysilane); those compounds with two or more benzene rings that are not fused, such as 2-hydroxy-4-(3-trialkoxysilylpropoxy)-diphenylketone, 3-hydroxy-4-(3-trialkoxysilylpropoxy)-diphenylketone, rosolic acid, 4-phenylazophenol, and 4-alkoxyphenylazobenzene-4-carboxy-alkyl triethoxysilane, primuline; and those with two or more benzene rings that are fused, such as trialkoxysilylpropyl-1,8-naphthalimide, anthraflavic acid, alizarin, quinizarin, 9-anthracene carboxy-alkyl triethoxysilanes (9-anthracene carboxy-methyl triethoxysilane, 9-anthracene carboxy-ethyl triethoxysilane, 9-anthracene carboxy-butyl triethoxysilane, 9-anthracene carboxy-propyl triethoxysilane, 9-anthracene carboxy-pentyl triethoxysilane), 9-anthracene carboxylic acid, 9-anthracene methanol and mixtures thereof.
According to another aspect of the present invention, methods for synthesizing absorbing spin-on-glass compositions are provided. Spin-on-glass materials are conventionally synthesized from silane and silicon-based reactants such as triethoxysilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, tetramethoxysilane, methyltrimethoxysilane, trimethoxysilane, dimethyldimethoxysilane, phenyltriethoxysilane, phenyltrimethoxysilane, diphenyldiethoxysilane, and diphenyldimethoxysilane. Halosilanes, particularly chlorosilanes, for example, trichlorosilane, methyltrichlorosilane, ethyltrichlorosilane, phenyltrichlorosilane, tetrachlorosilane, dichlorosilane, methyldichlorosilane, dimethyldichlorosilane, chlorotriethoxysilane, chlorotrimethoxysilane, chloromethyltriethoxysilane, chloroethyltriethoxysilane, chlorophenyltriethoxysilane, chloromethyltrimethoxysilane, chloroethyltrimethoxysilane, and chlorophenyltrimethoxysilane are also used as silane reactants.
A method of making an absorbing spin-on-glass composition includes combining one or more alkoxysilanes, or, one or more halosilanes, one or more incorporatable organic absorbing compounds, an acid/water mixture, such as a nitric acid/water mixture, and one or more solvents to form a reaction mixture; and refluxing the reaction mixture to form the absorbing spin-on-glass composition. The spin-on-glass composition so formed is diluted with one or more solvents to provide coating solutions that produce films of various thicknesses. Alternative methods of making an absorbing spin-on-glass composition, including methods using halosilanes and a phase transfer catalyst, are also provided.
In yet another aspect of the present invention, an absorbing spin on composition is produced comprising a silicon-based compound and an incorporatable organic absorbing compound that strongly absorbs light at wavelengths less than about 375 nm. Further provided are absorbing spin on compositions, wherein at least one of the silicon-based compound or the incorporatable organic absorbing compound comprises at least one alkyl group, alkoxy group, ketone group or azo group.
According to yet another aspect of the invention, the absorbing compounds of the chemical class comprising 9-anthracene carboxy-alkyl trialkoxysilane is provided. A method of synthesizing any one of the 9-anthracene carboxy-alkyl trialkoxysilanes includes combining 9-anthracene carboxylic acid, chloroalkyltrialkoxysilane, triethylamine, and a solvent to form a reaction mixture; refluxing the reaction mixture; cooling the refluxed reaction mixture to form a precipitate and a remaining solution; and filtering the remaining solution to produce liquid 9-anthracene carboxy-alkyl trialkoxysilane.